The present invention provides a method for manufacturing a calcined gypsum wherein the mixing water amount is reduced and the setting time does not increase. As a raw gypsum is compounded with a carboxylic acid-type material and calcined, a calcined gypsum can be manufactured wherein the mixing water amount is small and the setting time does not increase. Furthermore, a regular gypsum board can be manufactured without reducing the productivity of the gypsum board even if a large quantity of recycled gypsum causing increase of the mixing water amount is used as a raw gypsum, because the mixing water amount is small and the setting time does not increase for the calcined gypsum manufactured as described above.